Street Trees

The following is intended to be a short primer on which trees to use as street trees in South Florida and the Treasure Coast.

The list was compiled by reading through many publications, including those linked below, as well as discussions with arborists, landscape architects, horticultural experts, citizens, and more based on existing successes and failures in the actual landscapes of Palm Beach and Martin Counties. 

5 S’s to success:

  • Site
  • Soil
  • Spacing
  • Size
  • Species

Site:

In South Florida, it’s critical to remember we have a range of natural habitats. Not all plants will be happy near the ocean/intracoastal due to salt spray. Some trees will not thrive on the Atlantic Coastal Ridge sand dune (approximately between U.S.1 and I-95), and some species that are wind resistant in the East on well drained soil will topple in light winds in the former Everglades covering much of the county. All recommendations made below assume that irrigation will break, and that some soil compaction will occur in urban environments. Habitat types for each species are noted below.

Spacing:

The distance between tree trunks – also known as “pitch”. Street trees in South Florida should be spaced much closer together than is typical in other locations. This is primarily for two reasons: hurricanes and heat. Trees in closer proximity will protect each other from high winds, and in many cases, are capable of interlocking roots to add further wind resistance. Also, most trees take a more upright form when grown in close proximity (as they would grow in nature) – the branching structure is typically more perpendicular (as opposed to forming “y”s), This structure is more resistant to breaking to wind and therefore, providing both increased wind resistance and reduced maintenance (pruning y-branches).

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Secondly, to meet their basic infrastructure purpose for shade (critical safety and comfort functions for people walking and biking), denser, more resilient canopy cover is needed. In addition, the closer spacing enables them to better shade adjacent tree roots, increasing soil moisture. Tree pitch can also be used to encourage traffic safety – a change in spacing (eg, shifting from 24ft down to 18ft) will be perceived by drivers as an increase in speed, encouraging them to slow down as they enter into more pedestrian oriented areas. 

Never space trees > 24ft apart, or closer than 4ft, when used as street trees.

Soil:

Size – more is better. Trees do need [[square feet], but they can share. Each tree doesn’t need the full soil volume.

Pit Design – to get more soil, interconnect pits underground to enable them to “share” resources and interlock roots. Ensure soil is not compacted in the pit – engineered soil or devices like Silva cells can be used to create options in tight environments.

Type – Many of our trees do well in alkaline soil – we’re on limestone, which is similar to the impact from pouring concrete (free lime). This allows the use of more native trees – especially those that excel in the Keys.

Size: 
Although we are tempted to plant the biggest tree we can afford, this isn’t always the best answer. This may be an acceptable shortcut to get shade ASAP, but it does come with some penalties other than just cost. Large trees take a long time to establish – often many years. Smaller trees may in the meantime get established and be larger than the large trees 5 years out. Evidence also shows trees transplanted when large to be less wind resistant for the remainder of their lives than trees transplanted when small (or ideally, grown on site). When the space is available, more trees planted closer together will provide more resilient shade faster.

In terms of tree size at maturity, plant the biggest variety of tree that will fit in the location. If possible/practical, modify the location to enable bigger trees. Additional canopy area increases shading, cooling, water absorption (reducing sewer load), pollution mitigation, oxygen production, and carbon sequestration. 

Key

(N) – Native to Florida, “N?” indicates debate if the species is Native or was introduced by humans from nearby Carribean locations in the past.
(C) – Not known in FL prior to European settlement, but native to nearby Carribean locations. Typically evolved in habitats alongside existing tropical Florida Natives that migrated to FL from the Caribbean during the Holocene recent past
(I)  – Invasive potential, use cautiously
(O) – Other
(P) – Potential to use near power lines
(x-ft) – Spacing “pitch” in feeet recommended for planting to achieve shade goals

Species:

Spreading Canopy Trees: (Spaced every 18-24 feet)

  • (N, 20ft) Mahogany (Swietenia)
    • Trunk very wind resistant, but can drop large branches in hurricanes to shed wind
    • Species:
      • (N) Swietenia mahagoni – Native
      • (C) Swietenia macrophylla – Large leafed Caribbean species
  • (N, 20ft) Live Oak
    • Very Wind Resistant 
    • Species:
      • Quercus virginiana – Southern Live Oak
      • Quercus geminata – Sand Live Oak (slow growth, most wind resistant, minimal shade)
  • (C, 24ft) Rain Tree (Albizia saman) – Can get very large, maybe reserve larger spots
    • Fast growing, fairly wind resistant tree. Seems to do well in harsh environments or high water tables once established. 
  • (N, 18ft) Wild Tamarind (Lysiloma latisiliquum)
  • (C, N?, 20ft)  Black Olive (Bucida buceras
    • Very wind resistant, shapely, deep shade
    • Can leave black honeydew staining on sidewalks
  • (O, 24ft) Rusty fig (ficus rubiginosa)
  • (O, 6ft – 20ft, P) Podocarpus species (if you can find them available as tree forms)
    • Many cultivars are not appropriate as street trees.   
  • (N, 18ft) Jamaica-dogwood (Fish-fuddle) (Piscidia piscipula)
    • Do not plant near water
    • Prefers 10A or warmer
  • (O, 20ft) Azadirachta indica – (Neem) – Unkillable, wind resistant once established.
    • Has a bad reputation as it’s related to Chinaberry (an easily toppled-by-wind invasive) and traditionally coppiced creating weak wood. Municipalities in India recommend them for street trees in cyclone areas as a wind resistant option.
    • Only Plant Upland – does not get strong taproots on land with high water table
  • (O, 18ft) Teak
    • Large leaves
    • Uncommon and difficult to source, though it does well down in Miami, including near roads. (The Nursery that used to be Southeast Growers out in Wellington has some).  
    • Cold sensitive – USDA 10B or warmer

Medium Canopy Trees (Every 14-18 feet)

  • (N, 18ft) Paradise tree (Simarouba glauca) – beautiful native, female plants have fruits though
  • (C, 16ft) Shaving Brush Tree (Pseudobombax ellipticum)
  • (N, 14ft) Gumbo Limbo – often small canopy, but can excel in right conditions
  • (N, 14ft, P) Sea Grape (Coccoloba uvifera)
    • Very wind resistant but fruit can be messy
    • Trimmed to tree form can be very large
  • (N, 14ft?) Bald Cypress (Taxodium distichum.)
    • Taxodium mucronatum (24ft) is an evergreen relative, but availability is scarce. Breeding project ongoing in Tallahassee 
    • Taxodium ascendens (Pond Cypress)
    • Only gets “knees” when planted in a wet location. Very durable otherwise
  • (I, 10ft?, P) Hong Kong Orchid Tree (Bauhinia × blakeana hybrid)
    • No fruit, reduces mess
    • Very durable street tree, though sometimes tattered looking?
  • (O, 16ft) Beauty Leaf (Calophyllum)
    • Very wind resistant
    • Large, but *very* slow growth – 40 years
    • Cold sensitive – USDA 10B or warmer for full size
    • Selected Species:
      • Calophyllum inophyllum (mastwood, native to Asia)
      • Calophyllum brasiliense (native to Carribean)
      • (I) Calophyllum antillanum (invasive potential, native to Carribean)
  • (O, 14ft, P) Olive Tree (Olea europaea)
    • Super slow growing, but great otherwise
    • Does not fruit in humid locations
    • Recommended spacing closer unless large specimens are used
  • (N, 14ft, P) Pigeon Plum (Coccoloba diversifolia)
    • Very wind resistant
    • Typically dioecious, can select only male plants to avoid fruit
  • (N, 14ft) Scrub Hickory (Carya floridana)
    • Endemic to central Florida
    • Can be messy (nuts, leaf litter), semi-deciduous in south Florida
    • Very durable, wind resistant, beautiful shade tree
  • Longans (Dimocarpus longan) (O, 10ft, P) and Lychees (Litchi chinensis) (18ft)
    • Relatively wind resistant, edible fruits
    • Do OK on impacted soils once established, but often then won’t fruit (less mess)

Small-Canopy Trees 

Spacing 5-12 feet, depending on species

  • (N, 10ft) Autograph Tree (Clusia rosea)  – These actually make great shade trees. They are the big leafed relative of what people grow as hedges
  • (C, 12ft)Tabebuia impetiginosa: Purple Tabebuia
    • Very wind resistant
    • Very open canopy though
  • (C, 10ft, P) Tabebuia heterophylla: Pink Trumpet Tree
  • (N, 6ft, P) Yellow Elder (Tecoma stans)
    • May be difficult to source trees tall enough to act as street trees
  • (N, 8ft?, P) Bulnesia “Verawood” (Bulnesia arborea)
    • Sometimes looks a little tattered – under what conditions?
    • Yellow Flowers
  • Japanese Blueberry (Elaeocarpus decipiens)
  • Japanese Fern Tree (Filicium decipiens) 
  • (N, 6ft, P) Dahoon Holly (Ilex cassine)
  • (N, 6ft, P) East Palatka Holly (hybrid – I. cassine and I. opaca)
  • (N?, 6ft, P) Orange geiger
    •  
  • (C, 6ft, P) White geiger 
  • (O, 6ft), P) Ligustrum / Japanese Privet (Ligustrum japonicum)
    • Can work as a street tree if trained aggressively
  • (N, 5ft, P) Simpson’s Stopper (Myrcianthes fragrans)
    • Slow growing and must be trained to tree form
    • REQUIRES irrigation as a street tree
  • (O, 7ft, P) Weeping Bottlebrush (Callistemon viminalis)
    • Difficult to source / train tall enough to be a street tree
  • (O, 7ft, P) Madagascar Olive (Noronhia emarginata)

Trees to use cautiously: 

It’s not that you shouldn’t use these trees, but you shouldn’t use these trees as primary street trees without a good reason and a nuanced understanding of site conditions (eg, power lines, saltwater intrusion in soil, etc). You can always interspace palms and smaller ornamental trees, but only if the primary shade habitat needs are already met.

  • (N, 10ft, P – silver only) Buttonwood (Conocarpus erectus)
    • Grow in all soils and impacted ground, but prefer wet soil
    • Green variety grow WAY faster than the Silver variety
    • Not very wind resistant (trunks snap in high winds)
    • Only Green variety grows quickly
  • (N, 10ft) Satinleaf (Chrysophyllum oliviforme)
    • Beautiful tree with dense shade
    • Tends towards smaller form in the urban environment
    • Needs consistently moist soil, or can be planted as an understory tree
    • Does not do well if not kept wet
  • (N, C, 14-24ft) Other Oak (Quercus) species
    • Eg, native Quercus laurifolia, hybrids, etc
    • Many have root issues, wind performance, but common hybridization complicates proper selection
  • (I, 16ft) Tropical Almond  (Terminalia catappa) –
    • Un-killable, VERY wind resistant, though cold sensitive (USDA 10A or warmer)
    • I visited Puerto Rico before and after Hurricane Maria – these had almost 100% survival
    • Large fruit/nut/leaf caveat, so maybe not great over parking
  • (C, 20ft) Silk floss tree (Ceiba speciosa)
    • Medium to large tree, common street tree in Buenos Aires and SE Asia, but has thorns on trunk (prevents vandalism though…), tends to lose leaves for a few weeks in August though
  • (O, 12ft, P) Queen Crape Myrtles
    • Although attractive in landscape environments, they often fail to provide much shade or large canopy in urban environments as soil is compacted, irrigation fails, and the real world happens. They also tend to look tattered much of winter leading to complaints.
  • (N, 14ft?, P) Lysiloma sabicu
    • Maybe for use under power lines
    • Somewhat weeping form limits uses
    • Does well on coral-limestone soils
  • (N, 16ft) Red maple
    • Relatively small native, loses leaves for much of the year 
    • Prefers moist soil
  • (N, 14ft?) Florida Soapberry
  • (N, 12ft?, P) Florida Fiddlewood (Citharexylum spinosum)
    • Can be hard to keep trained into tree form
  • (N, 8ft, P) Sweet Acacia (Vachellia farnesiana)
    • Most nursery stock is variety with thorns
    • Slow growing
    • Beautiful yellow flowers
  • (O, 8ft, P) Natal Plum
    • Thorns mean additional maintenance concerns
    • Slow growing, but many very large relatively affordable specimens available from nurseries since it was historically more popular

Median or “Tree Box” Trees (large, aggressive roots, poisonous, or not good shade, etc):

  • (C) Kapok (Ceiba pentandra) , Bombax ceiba
    • Used as a street tree (even in small medians) in Latin America,
    • Roots have uplift potential in many soils, would need probably 2′ root block / curb to contain  
  • (N, C, I) Other Ficus species
    • Typically wind resistant (except ficus benjamina)
    • Again, roots can be contained with proper planter design
  • Real Tamarind (tamarindus indica)
    • Very wind resistant
    • Messy (edible) fruit
  • Mangos (Mangifera indica)
    • Very wind resistant
    • Typically not used due to mess, allergies
  • (N) False Mastic Tree (Sideroxylon foetidissimum)
    • Very wind resistant
    • Tallest native florida tree
    • Diecious – females drop messy latexy fruit, but males do not have fruit
    • Mixed reaction to the smell of the flowers, often said to be like “cheese”
  • (C) Albizia niopoides
    • Tallest tree in FL
  • Rainbow Eucalyptus
    • Size limited in SoFlo (only up to 60 ft tall)
    • Pyramidal crown
    • Only Plant Upland – does not get strong taproots on land with high water table
  • Royal Poinciana
    • Readily drops large branches in high winds. 
    • Potential to use as a “nursery tree” on minor streets (eg, paired with alternating oaks)
  • (N) Slash Pine
  • Jacaranda
    • Unreliable as a shade tree
    • Beautiful flowers